Not applicable.
Not applicable.
The invention relates to a projection objective with at least two waists and three bulges, as was developed for microlithography and for example is known from the patent application (not prior published) xe2x80x9cMikrolithographisches Reduktionsobjectiv, Projektions-belichtungs-Anlage und-Verfahrenxe2x80x9d (xe2x80x9cMicrolithograpbic Reduction Objective, Projection Exposure Equipment and Processxe2x80x9d) of the invention priority of the same priority date, and the documents cited therein. An example therefrom is, e.g., U.S. patent application Ser. No. 09/416,105. This application and the documents cited therein are incorporated herein by reference.
The required reduction in size of the projected structures leads to working with progressively lower wavelengths of the light used. Of importance here are the excimer laser sources at 248 nm, 193 nm and 157 nm.
While purely quartz glass objectives are usable at 248 nm, a partial achromatization is required at 193 nm because of the increasing dispersion of quartz glass, and calcium fluoride is available as a second material for combination with quartz glass for this purpose.
However, calcium fluoride lenses have to be used as sparingly as possible for various reasons, from the availability of large, homogeneous crystals to the feasibility of optical processing.
It makes little sense to reduce the wavelengths and introduce completely new system technologies if the numerical aperture is not kept up to the high level attained (above 0.6, preferably 0.65 and more), since the resolution is in fact determined by the quotient lambda/NA.
For other wavelengths also, particularly for purely quartz glass DUV systems, an increase of the numerical aperture is sought, without a further increase of the lens diameter, since the limits of production feasibility are then also reached.
The invention therefore has as its object to provide a projection objective that makes possible the highest numerical aperture with the smallest lens diameter, taking note of the additional properties required in a microlithographic projection objective.
This object is successfully attained by the following measures that relate to the lens groups situated after the second waist and in front of the image, to the position of the system diaphragm, and to the constitution of the diaphragm space, and provide for a novel constriction (beam waist, reduction of beam diameter) there.
The projection objective has a lens arrangement with a first positive lens groups (LG1), a first negative lens group (LG2), a second positive lens group (LG3), a second negative lens group (LG4), and a further lens arrangement (LG5-LG7) containing a system diaphragm (AS), wherein at least one of the two next lenses before or after said system diaphragm AS has negative refractive power.
The projection objective includes a lens arrangement with: a first positive lens group (LG1), a first negative lens group (LG2), a second positive lens group (LG3), a second negative lens group (LG4), a further lens arrangement (LG5-LG7) containing a system diaphragm (AS), and at least three lenses before said system diaphragm (AS).
The projection objective with a lens arrangement has a first positive lens group (LG1), a first negative lens group (LG2), a second positive lens group (LG3), a second negative lens group (LG4), a further lens arrangement (LG5-LG7) containing an system diaphragm (AS), and at least one spherically over-correcting air space between adjacent lenses in front of said system diaphragm (AS).
The projection objective with at least two waists and three bulges, has a system diaphragm (AS) arranged in a region of a last bulge on an image side of said projection objective, and a pair of lenses before or after said system diaphragm (AS), wherein at least one lens of said pair of lenses is negative.
Advantageous possible combinations of the above measures according to the invention are shown in the preferred embodiments.
A particularly advantageous embodiment of the invention has a high numerical aperture of above 0.65 or 0.70. This can indeed count as an object that is always set per se; however, it is an outstanding feature of the invention that these values are reliably attained, and indeed under otherwise usable conditions such as image field and the like.
An advantageous construction according to the invention is an objective of a single material, in particular a quartz glass objective such as is provided for DUV at 248 nm. An advantageous embodiment has two different lens materials. A partially achromatized objective (e.g., for 193 nm) with quartz glass and calcium fluoride is an advantageous embodiment. The wide applicability of the objective design is apparent from this, and it can also be applied to other wavelengths, such as 365 nm or 157 nm, eventually using other lens materials.
In an advantageous embodiment of the correction means of the negative lens in the diaphragm space, the negative lenses are provided on both sides of the aperture diaphragm.
Advantageously, there are likewise provided in this region two spherically over-correcting air spaces, the middle thickness of which is thus greater than the thickness at the edge.
An advantageous constructional feature for the region of the first positive lens group includes two negative lenses provided among the first three lenses on the object side, preferably the first lens being negative. This helps to reach high apertures with good Petzval correction.
Advantageously, the projection objective according to the invention is incorporated in a projection exposure equipment for microlithography, with which an increased imaging performance can be effected, for example, with laser light at 248 nm or 193 nm, within the scope of conventional constructions.
An advantageous process for the production of microstructured components, with such a projection exposure equipment and a projection objective is as follows: exposing a substrate provided with a photosensitive layer by a mask and a projection objective and structuring the photosensitive layer corresponding to a pattern contained on said mask.